Hydrated goethite (α-FeOOH) (1 0 0) interface structure: Ordered water and surface functional groups     

Sanjit K. Ghose  Glenn A. Waychunas  Peter J. Eng 《Geochimica et cosmochimica acta》2010,74(7):1943-2587

Goethite(α-FeOOH), an abundant and highly reactive iron oxyhydroxide mineral, has been the subject of numerous studies of environmental interface reactivity. However, such studies have been hampered by the lack of experimental constraints on aqueous interface structure, and especially of the surface water molecular arrangements. Structural information of this type is crucial because reactivity is dictated by the nature of the surface functional groups and the structure or distribution of water and electrolyte at the solid-solution interface. In this study we have investigated the goethite (1 0 0) surface using surface diffraction techniques, and have determined the relaxed surface structure, the surface functional groups, and the three dimensional nature of two distinct sorbed water layers. The crystal truncation rod (CTR) results show that the interface structure consists of a double hydroxyl, double water terminated interface with significant atom relaxations. Further, the double hydroxyl terminated surface dominates with an 89% contribution having a chiral subdomain structure on the (1 0 0) cleavage faces. The proposed interface stoichiometry is ((H₂O)(H₂O)OH₂OHFeOOFeR) with two types of terminal hydroxyls; a bidentate (B-type) hydroxo group and a monodentate (A-type) aquo group. Using the bond-valence approach the protonation states of the terminal hydroxyls are predicted to be OH type (bidentate hydroxyl with oxygen coupled to two Fe³⁺ ions) and OH₂ type (monodentate hydroxyl with oxygen tied to only one Fe³⁺). A double layer three dimensional ordered water structure at the interface was determined from refinement of fits to the experimental data. Application of bond-valence constraints to the terminal hydroxyls with appropriate rotation of the water dipole moments allowed a plausible dipole orientation model as predicted. The structural results are discussed in terms of protonation and H-bonding at the interface, and the results provide an ideal basis for testing theoretical predictions of characteristic surface properties such as pK_a , sorption equilibria, and surface water permittivity.  相似文献   

Leaky savannas: the significance of lateral carbon fluxes in the seasonal tropics          下载免费PDF全文

Sarah Tweed  Marc Leblanc  Adrian Bass  Glenn A. Harrington  Niels Munksgaard  Michael I. Bird 《水文研究》2016,30(6):873-887

Globally, dissolved inorganic carbon (DIC) accounts for more than half the annual flux of carbon exported from terrestrial ecosystems via rivers. Here, we assess the relative influences of biogeochemical and hydrological processes on DIC fluxes exported from a tropical river catchment characterized by distinct land cover, climate and geology transition from the wet tropical mountains to the low‐lying savanna plains. Processes controlling changes in river DIC were investigated using dissolved organic carbon, particulate organic carbon and DIC concentrations and stable isotope ratios of DIC (δ¹³C_DIC) at two time scales: seasonal and diel. The recently developed Isotopic Continuous Dissolved Inorganic Carbon Analyser was used to measure diel DIC concentration and δ¹³C_DIC changes at a 15‐min temporal resolution. Results highlight the predominance of biologically mediated processes (photosynthesis and respiration) controlling diel changes in DIC. These resulted in DIC concentrations varying between 3.55 and 3.82 mg/l and δ¹³C_DIC values ranging from ?19.7 ± 0.31‰ to ?17.1 ± 0.08‰. In contrast, at the seasonal scale, we observed wet season DIC variations predominantly from mixing processes and dry season DIC variations due to both mixing processes and biological processes. The observed wet season increases in DIC concentrations (by 6.81 mg/l) and δ¹³C_DIC values of river water (by 5.4‰) largely result from proportional increases in subsurface inflows from the savanna plains (C₄ vegetation) region relative to inflows from the rainforest (C₃ vegetation) highlands. The high DIC river load during the wet season resulted in the transfer of 97% of the annual river carbon load. Therefore, in this gaining river, there are significant seasonal variations in both the hydrological and carbon cycles, and there is evidence of substantial coupling between the carbon cycles of the terrestrial and the fluvial environments. Recent identification of a substantial carbon sink in the savannas of northern Australia during wetter years in the recent past does not take into account the possibility of a substantial, rapid, lateral flux of carbon to rivers and back to the atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Where Is It and Where Is It Going? A Comprehensive Look at GPS Asset Location Systems,Part 2     

John W. Lavrakas  Glenn C. Marshall 《GPS Solutions》1995,1(2):121-128

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Jupiter’s Great Red Spot: compactness condition and stability     

Jun-Ichi Yano  Glenn R. Flierl 《Annales Geophysicae》1994,12(1):1-18

Linear Rossby wave dispersion relationships suggest that Jupiter’s Great Red Spot (GRS) is a baroclinic structure embedded in a barotropic shearing zonal flow. Quasi-geostrophic (QG) two-layer simulations support the theory, as long as an infinitely deep zonal flow is assumed. However, once a finite depth of the lower layer is assumed, a self-interaction of the baroclinic eddy component produces a barotropic radiating field, so that the GRS-like eddy can no longer remain compact. Compactness is recovered by explicitly introducing a deep dynamics of the interior for the lower layer, instead of the shallow QG formulation. An implication of the result is a strong coupling of the GRS to a convectively active interior.Paper presented to the NP Symposia of the 1991 Wiesbaden EGS Assembly on “Nonlinear processes in Geophysics”  相似文献   

Numerical studies of barotropic modons   总被引：1，自引：0，他引：1  

James C. McWilliams  Glenn R. Flierl  Vitaly D. Larichev  Gregory M. Reznik 《Dynamics of Atmospheres and Oceans》1981,5(4):219-238

Numerical solutions of barotropic modons are examined to assess the accuracy with which they can be calculated, their behavior under the influence of dissipation, and their resistance to perturbations.  相似文献   

Simple applications of McWilliams' “A note on a consistent quasigeostrophic model in a multiply connected domain”     

Glenn R. Flierl 《Dynamics of Atmospheres and Oceans》1977,1(5):443-453

We have solved several linear quasigeostrophic problems in singly and multiply connected domains to illustrate the use and effects of correct boundary conditions which balance circulation changes with forcing along each boundary. The results with these boundary conditions differ markedly from those obtained by setting the streamfunction to zero on the walls either when the fluid is forced by a time-dependent wind stress curl or when the fluid oscillates in a free basin mode in a domain which contains interior islands.  相似文献   

Plume dynamics, thermal energy and long-distance transport of vulcanian eruption clouds from Augustine Volcano, Alaska     

Juergen Kienle  Glenn E. Shaw 《Journal of Volcanology and Geothermal Research》1979,6(1-2)

Augustine, an island volcano in Lower Cook Inlet, southern Alaska, erupted in January, 1976, after 12 years of dormancy. By April, when the eruptions ended, a new lava dome had been extruded into the summit crater and about 0.1 km³ of pyroclastics had been deposited on the island, mainly as pyroclastic debris avalanches and pumice flows. The ventclearing phase in January was highly explosive and we have been able to document 13 major vulcanian eruptions.The timing, thermal energy, mass loading of fine particles and the horizontal dispersion of these eruption clouds were determined from radar measurements of cloud height, reports of pilots flying in plumes, satellite photography, seismic records and infrasonic detection of air waves. A lower estimate of the mass of fine (r < 68 μm) particles injected into the troposphere from the 13 main eruptions in January is 5.5–18 × 10¹² g. The corresponding mass loading of fine particles within individual eruption clouds is 0.3–1 g m⁻³. We calculated thermal energies of 4 × 10¹⁴ to 35 × 10¹⁴ J for individual eruptions by applying convective plume rise theory to observed cloud heights and seismically determined eruption durations. This energy range compares favorably with the 4–16 × 10¹⁴ J of thermal energy, calculated from the cooling of juvenile material contained in a typical eruption cloud.The vulcanian eruption clouds stayed intact for at least 700 km downwind. Satellite images in both visible and infrared wavebands, showing the Gulf of Alaska just after sunrise on January 23, reveal a series of puffs strung out downwind from the volcano, 20–30 km in diameter and with their tops at altitudes of about 8 km, overlying a continuous plume at altitude 4 km. Each puff corresponded to a seismically and infrasonically timed eruption. A substantial portion of the material injected into the atmosphere between January 22 and 25 was rapidly transported by the subpolar jet stream through southwestern Canada and the western United States, then northeast across the States into the Atlantic. The clouds were observed passing over Tucson, Arizona, on January 25 at an elevation of 7 km.Several of the eruptions penetrated into the stratosphere. Sun photometer measurements, taken at Mauna Loa, Hawaii, six weeks after the eruption, showed an increased stratospheric optical thickness of 0.01 (wavelength 0.5 μm), which decayed in about 5 months. The maximum column mass loading of the veil was 4–10 × 10⁻⁷ g cm⁻². The mass of the veil, spread-ever a fourth of the earth's surface, is 10 to 100 times larger than can be accounted for by assuming that injected ash and converted sulfate particles from the 13 main Augustine eruptions are the only components contributing to the stratospheric turbidity observed at Mauna Loa.  相似文献   

Some aspects of vortices in rotating stratified fluids     

Glenn J. Shutts  Alan J. Thorpe 《Pure and Applied Geophysics》1978,116(6):993-1006

Summary Ideas concerning the overturning of unstably stratified, rotating fluids are explored using potential vorticity.A set of equations governing axi-symmetric flow in a quasi-Boussinesq system are found based on the gradient wind approximation, and a transformation analogous to that developed byHoskins [6] is used.The time-development of a linear, thermally unstable vortex under the action of Ekman pumping is studied with these equations. The changing radial scale during amplification of the vortex is well represented.Finally, some exact steady vortex states for stably stratified fluids are found and their possible relevance to atmospheric vortices is discussed.  相似文献   

Seasonal and environmental variations in sediment accretion in a Long Island salt marsh     

Glenn A. Richard 《Estuaries and Coasts》1978,1(1):29-35

Flax Pond is a small (0.5 km²) salt marsh on the north shore of Long Island, New York. Two 1 m² plots within each of the following environments were covered with a marker layer of either brick dust or aluminum glitter: 1) bare mud flats; 2) areas newly colonized by Spartina alterniflora; and 3) high intertidal. S. alterniflora peat surfaces. Monthly cores revealed the amount of sediment that accumulated since placement of the marker. Accretion rates from October, 1974 to February, 1976 were as follows: bare mud flats ?20.5 to 45.5 mm/yr; recently vegetated mud flats ?9.5 to 37.0 mm/yr; and high intertidal peat surfaces ?2.0 to 4.25 mm/yr. Sedimentation rates decrease with increasing elevation because of the reduced tidal submergence time and decreased height of the overlying water column. In areas of low elevation, ice and storms cause either erosion or a reduced rate of accretion during the winter months. The average mud accretion rate over the past 173 years is 3.4 mm/yr. Differences between the short-term rate and the long-term rate indicate substantial annual variation in the accumulation of mud in salt marshes. Short-term rates of peat accretion are similar to long-term estimates, indicating that rates of peat accretion are relatively constant over long intervals.  相似文献   

Uranium series dating of stalagmites from Blanchard Springs Caverns,U.S.A.     

Glenn M. Thompson  David N. Lumsden  Raymond L. Walker  Joel A. Carter 《Geochimica et cosmochimica acta》1975,39(9):1211-1218

Because stalagmites are enriched in ²³⁴U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, ²³⁴U/²³⁸U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP.  相似文献